Fully automated on-line flow-batch based ultrasound-assisted surfactant-mediated extraction and determination of anthraquinones in medicinal plants

Two easily performed procedures - one sequential injection (SIA) and the other stepwise injection (SWIA) - based on on-line ultrasound-assisted surfactant-mediated extraction followed by spectrophotometric determination of total anthraquinones in medicinal plants are presented. Powdered samples containing Frangula alnus (cortex) and Rubia tinctorum (roots and rhizomes) were placed in the bottom of an extraction chamber connected to an automatic manifold; the chamber was then immersed into an ultrasonic bath and a solution of Triton X-100 was applied as the extraction medium at 75 °C and under ultrasonication. The extract was submitted on-line for spectrophotometric detection at 435 nm wavelength, and the content of anthraquinones was evaluated using Alizarin as the calibration standard. The linear ranges were up to 0.05 and 0.2 g L− 1 of Alizarin, and the detection limits, calculated as 3 s of a blank test (n = 10), were found to be 0.55 mg L− 1 for SIA and 4 mg L− 1 for SWIA, respectively. The relative standard deviation, assessed through ten replicate measurements of real samples, varied in the range 1.1-4.6% for both developed procedures. The suggested procedures were validated according to reference methods. The sampling frequencies were 12 h− 1 for SIA and 6 h− 1 for SWIA, respectively.